This section provides background information related to the present disclosure which is not necessarily prior art.
Methicillin resistance of Staphylococcus aureus (MRSA) is determined by the mecA gene which is carried by a mobile genetic element, designated staphylococcal cassette chromosome mec (SCCmec). MecA encodes a beta-lactam-resistant penicillin-binding protein called PBP2a (or PBP2′). Beta-lactam antibiotics normally bind to PBPs in the cell wall disrupting the synthesis of the peptidoglycan layer which results in bacterium death. However, since the beta-lactam antibiotics cannot bind to PBP2a, synthesis of the peptidoglycan layer and the cell wall continues. While the mechanism responsible for mecA transfer is still obscure, evidence supports horizontal transfer of the mecA gene between different staphylococcal species. Typically MRSA is diagnosed using culture based methods.
The Clinical and Laboratory Standards Institute (CLSI) recommends the cefoxitin disk diffusion test supplemented with the latex agglutination test for PBP2a. Phenotypic expression of resistance can vary depending on the growth conditions, as well as on the presence of subpopulations of staphylococci that may coexist (susceptible and resistant) within a culture making susceptibility testing by standard microbiological methods potentially problematic. In addition, culture takes time, usually 1 to 5 days. Faster techniques of MRSA screening by molecular methods, such as Polymerase Chain Reaction (PCR), have been developed to test for the mecA gene that confers resistance to methicillin, oxacillin, nafcillin, and dicloxacillin and other similar antibiotics. Such techniques, while faster, still take hours and are sent out to labs. In addition, commercially available molecular approaches (used for screening) are unable to detect mecA-variants of MRSA.
Raman spectroscopy is a reagentless, non-destructive, technique that can provide the unique spectral fingerprint of a chemical and/or molecule allowing for target identification without sample preparation. With this technique, a sample is irradiated with a specific wavelength of light whereby a small component, approximately 1 in 107 photons, is in-elastically scattered (at wavelengths shifted from the incident radiation). The inelastic scattering of photons, due to molecular vibrations that change the molecule's polarizability, provide chemical and structural information uniquely characteristic of the targeted substance. Raman Spectroscopy can be extremely useful in fully characterizing a material's composition, and allows for relatively fast identification of unknown materials with the use of a Raman spectral database. In addition, since Raman Spectroscopy is a non-contact and non-destructive technique, it is well suited for in-situ, in-vitro and in-vivo analysis.
Raman Spectroscopy has high potential for screening of bacteria, virus, drugs, as well as tissue abnormalities since it: 1) is practical for a large number of molecular species; 2) can provide rapid identification; and 3) can be used for both qualitative and quantitative analysis. A portable or handheld micro Raman based detection instruments would be useful to reliably and rapidly assess Staphylococcus aureus strains in wounds or nasal passages. Rapid assessment and typing would enable tracking the spread of such pathogens and could significantly decrease the number of hospital-acquired infections and the associated costs in treatment thereof.